What's wrong with your 5D mkii? Would a better use of the cash be on a nice new lens, or maybe a photographic trip of a lifetime?

Personally, i think i'd go with the 5D mkiii if i had to choose out of the two. My thinking being that because it's newer it's probably got better technology on the focus, noise reduction and processor fronts.

In reply to Dispater: I'd go for the 5diii, even though mine did die in the rain , to be fair it was chucking and the spray from the river was giving it a good soaking from every angle . I looked at the 1dsiii but decided that for most of what i do i dont need the bulk of 1ds or 1dx . The 5diii is a significant improvement on the 5ii, being better at low light and 6fps rather than 3fps makes a difference for action shots . the price has come down a lot in the past few months for the 5iii, so more realistic than a 1dx.

In reply to Dispater: I think i was just unlucky , my 5ii had been through all sorts of crap with water coming out of the side ports and it was fine yet I've heard of other peoples 5ii dying in a drizzle . You'll be very happy with the 5iii, very sharp straight out of camera , sensitive autofocus even at the side points and great low light .

In reply to Dispater: 5D III has same AF module as 1D X, just lacks the second AF sensor and processor. 5D III sensor is incredible, heaps better than a 1Ds III. 5D's weather sealing is specced the grade below a 1D XYZ but the grade above a Mk II (straight from Canon, not opinion) ISO performance of 5D Mk III is pretty great but weirdly the EOS 6D has been proven better for ultra high ISO use, astrophotographers are now all switching to 6D's, shame the build quality is absolute carp.

Water damage is a pretty cruel mistress but a carrier bag with an elastic band is a perfect rain coat ;)